Project Summery Alzheimer's disease (AD) represents a major medical, public health, and health system crisis. In the United States, AD is the 6th leading cause of death, killing more than breast cancer and prostate cancer combined. AD currently afflicts 5.1 million Americans and prevalence is expected to triple by 2050. The need for early diagnosis and treatment of AD is widely recognized as a high unmet need and is therefore the focus of major pharmaceutical and diagnostic companies. In this proposal we will develop a novel cerebrospinal fluid (CSF) and blood assays to address the need for early identification of patients at risk for cognitive deterioration in AD. Building on prior work, our assays hold the potential for early stratification of patients at risk for AD and for monitoring response to therapy. The proposed tests are based upon our laboratory's discovery that measured levels of the NPTX2protein found in CSF are associated with their cognitive status. We aim to develop a pre-commercial prototype ELISA assay and evaluate expanded clinical patient samples to evaluate the further utility and analytical parameters of the NPTX2 assays in CSF. We will also evaluate blood-based assays of NPTX2. Critical milestones include: 1) Validate the sensitivity, specificity and reproducibility of NPTX2 ELISA using human CSF. 2) Assess the utility of NPTX2 measures in CSF in ~190 human cerebrospinal fluid samples from patients monitored by the Alzheimer's disease research center (ADRC) at University of California San Diego (UCSD) to distinguish control from AD subjects in a cross-sectional analysis, and determine the value of CSF NPTX2 measures to predict progression of cognitive failure in longitudinal follow-up. 3) Evaluate the performance of CSF NPTX2 relative to other biomarkers that are widely used in the diagnosis of AD including A42, tau, phospho-tau, and synaptic proteins. We will test hypotheses from our published work that NPTX2 provides unique information regarding the ?resilience? of the brain to effects of A amyloid and tau, and that a combined measure that includes NPTX2 can enhance the diagnostic performance of tau (Xiao et al., 2017). 4) Additionally, we will optimize methods for the isolation and assay of brain-derived exosomes from blood plasma and assess efficacy of plasma NPTX2 measures to distinguish AD patients from normal controls. Findings will provide a basis for negotiations with potential corporate sponsors including bio techne (see letter of support), and Roche Diagnostics GmbH, and will be evaluated as a basis, in part, for a new company, CogNext Diagnostics.